The present invention relates to a method for separating food pieces in a liquid based upon differences in specific gravity of the food pieces. In particular, the present invention relates to a method for separating young food particles from mature food particles in a liquid based upon the starch content of the food particles.
Sweetness is a primary attribute of peas that is of concern to consumers. Pea sweetness depends upon the sugar content within the pea which is itself a function of pea maturity. A pea matures when sugars initially present within the pea are converted to starch for long term energy storage. In addition to sweetness, the amount of starch within the pea also affects the texture or mouthfeel of the pea. Consumers prefer a tender mouthfeel which translates into a smooth firm texture. As starch concentration increases within the pea, the pea tends to take on a rough texture.
Pea maturity as measured by starch concentration has been measured by a wet chemistry test that determines the percentage of Alcohol Insoluble Solids (AIS) within the pea. As a pea matures, the amount of the alcohol insoluble solids within the pea increases while the amount of alcohol soluble solids decreases. AIS units may be correlated with the percentage of starch within the peas. For example, early peas which are usually high in sugar content have low starch concentrations and therefore have a low AIS percentage, whereas mature peas picked later in the season have high starch concentrations and therefore have a high AIS percentage.
The accepted procedure for the calculation of AIS is designated as "Solids (Alcohol-Insoluble) in Frozen Peas, Gravimetric Method", 32.065 of the Association of Official Chemists. In addition to the AIS test, an instrument known as a Tenderometer, available from the FMC Corporation of Summit, Ill., is used to provide an initial rough estimation of the quality of a batch of peas based upon the relative tenderness of the peas.
As sugar is converted by the peas into starch, the specific gravity of the peas increases since starch in situ is a more dense compound than sugar. Because of this difference in specific gravity, mature peas have been separated from young, high sugar peas by formulating a brine solution of intermediate specific gravity calculated from data obtained by the AIS test and the use of the Tenderometer. The peas are dispersed into the static brine solution and the more mature peas with a high starch concentration and specific gravity in a high range tend to sink to the bottom of the brine solution. Younger, higher sugar content peas with a low starch concentration and specific gravity in a low range tend to float.
The use of a brine solution having a sodium chloride concentration of at least about thirteen weight percent poses problems. One of these problems includes corrosion of equipment contacted with the brine. The high salt concentration can cause metals within the pea separator to corrode which may effect the taste of the peas. In addition, there is a great problem of disposing of the brine solution after it has been used. Waste brine has a prohibitively high concentration of chloride ions in that environmental regulations make the waste brine difficult or impossible to discharge in some states.
The Adams et al. patent, U.S. Pat. No. 5,039,534, describes an apparatus and a method for separating peas based upon differences in pea specific gravity. The apparatus includes a flow trough having a flow manifold and a series of vanes to distribute water to create a laminar flow within the trough. Peas entering the trough are carried off and classified by settling velocity in the laminar flow region. The settling velocity is dependent upon both specific gravity and pea particle size. Peas having a high settling velocity settle into a first collection chamber. Peas having a lower settling velocity settle into a second collecting chamber.